• Carbon letters
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• 제9권1호
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• pp.23-27
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• 2008

The adsorption and reduction of Cr (VI) to Cr (III) by surface modified activated carbon (AC) in an aqueous solution was studied. The effects of surface modifications on the properties of the carbons were investigated by the analysis of specific surface area, carbon surface pH, acid/base surface values and functional groups. In order to understand the Cr(VI) adsorption and reduction ratio from Cr(VI) to Cr(III), the Cr adsorption capacity of AC was also measured and discussed by using inductively coupled plasma and UV spectrophotometer. The modifications bring about substantial variation in the chemical properties whereas the physical properties such as specific surface area, pore volume and pore size distribution nearly were not changed. Total Cr adsorption efficiency of as-received activated carbon (R-AC) and nitric acid treated activated carbon (N1-AC and N2-AC) were recorded on 98.2, 99.7 and 100%. Cr(III) reduction efficiency of R-AC increased largely from 0.4% to 28.3% compared to N1-AC and N2-AC.

• 대한화학회지
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• 제61권2호
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• pp.77-81
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• 2017

• 대한화학회지
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• 제55권3호
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• pp.418-429
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• 2011

[ $N^1,N^2$ ]bis(3-((3-hydroxynaphthalen-2-yl)methylene-amino)propyl)phthalamide ($H_4L$, 1) 의 새로운 크롬(III), 망간(II), 철(III), 코발트(II), 니켈(II), 구리(II), 루테늄(III) 및 산화 지르코늄(II) 착물을 합성하여 원소분석, 물리적 성질 및 분광학적으로 특성을 규명하였다. 분광학적 결과를 통해 이 리간드는 $[H_4LMX_2(H_2O)]{\cdot}nH_2O$ (M = Cu(II), Ni(II), Co(II), X = Cl 또는 $NO_3$)의 일반식을 갖는 착물2-5에서는 중성의 삼배위 리간드로 행동한다. 또는 $[H_4L(ZrO)_2Cl_2]{\cdot}8H_2O$ 의 일반식을 갖는 착물 6-9 에서는 이염기성 육배위 리간드로 행동한다. DMF 용액에서의 몰전기전도도 실험결과 이들 착물은 비이온성을 나타낸다. 고체 구리착물 2, 5 및 6 의 ESR 스펙트럼에서 $g_{\parallel}$ >g> $g_e$을 보이는데, 이는 일그러진 팔면체구조와 큰 공유결합성을 갖는 $d{_x}^2{_{-y}}^2$ 오비탈에 비공유 전자쌍이 존재함을 의미한다. 이합체 구리(II) 착물 $[H_2LCu_2Cl_2(H_2O)_4]{\cdot}3H_2O$ (6)에 대해 두 구리원자 사이의 거리를 ESR 스펙트럼으로부터 추정한 parallel component 의 field zero splitting 파라메타를 이용하여 계산하였다. 이들 화합물의 항박테리아 및 항균 활성도를 측정한 결과, 몇가지 금속 착물의 경우 표준시약인 tetracycline (박테리아) 및 Amphotricene B (균류)보다 더 큰 저해효과를 보였다.

• 대한화학회지
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• 제28권2호
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• pp.95-101
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• 1984

$cis - [Cr(en)_2Cl_2]^+ $착물의 수화반응에 대한 연구를 전기전도도법에 의해. 온도는 $15^{\circ}C{\sim}30^{\circ}C$에서 압력은 $1{\sim}2000bar$의 범위에서 실시하였다. 반응속도는 온도가 증가함에 따라 증가하고, 압력이 증가하면 감소하였다. 활성화부피(${\Delta}V^{\neq}$)는 $25^{\circ}C$, 1bar에서 $1.82cm^2/mole$로 비교적 작은 양의 값을 나타내었으며, 이 값은 압력이 증가함에 따라 감소하고 온도 증가에 따라서는 증가하였다. 활성화엔트로피(${\Delta}S^{\neq}$)$는 $25^{\circ}C$, 1bar에서 -9.019 eu로 작은 음의 값을 나타내었다. 활성화파라미터의 값으로부터 수화반응의 메카니즘은 교환해리(Id)메카니즘인 것으로 밝혀졌다.

• 대한치과보철학회지
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• 제34권1호
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• pp.143-150
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• 1996

The purpose of this study was to evaluate the tensile strength of solder joint between gold alloy and nickel-chromium alloy. The specimens were made with type III gold alloys and Ni-Cr-Be alloy and Degular Lot 2 solder. Eighteen paired specimens were made, and subdivided into three groups. Group I specimens were gold alloy-gold alloy combination, Group II specimens were gold alloy-Ni-Cr alloy combination, Group III specimens were Ni-Cr alloy-Ni-Cr alloy combination. Solder block were made with solder investment(Degussa A,G, Germany) and stored in room temperature for 24 hours. To reduce the formation of metallic oxide and increase wetting properties, flux was used before preheating and soldering procedure. The specimens were preheated at $650^{\circ}C$ and flux were applied again and gas-oxygen torch was used to solder the specimen. All soldered specimens were subjected to a tensile force in the Instron universal testing machine : the crosshead speed was 1 mm/mim. Tensile strength values of three soldered joint groups were 1. Gold alloy-Gold alloy solder joint : $$48.8kg/mm^2$$ 2. Gold alloy-Ni-Cr alloy solder joint : $$30.9kg/mm^2$$ 3. Ni-Cr alloy-Ni-Cr alloy solder joint : $$31.8kg/mm^2$$ The microscopic examination of fracture site showed cohesive and combination fracture modes in gold alloy specimens, but showed all adhesive fracture modes in Ni-Cr alloy containing specimens.

• 대한화학회지
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• 제30권2호
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• pp.181-187
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• 1986

$trans-Cr^{Ⅲ}N_4XY$착물의 광화학적 치환반응에 있어서 한개의 리간드가 떨어져서 생기는 가상적 1차중간체의 총안정화에너지를 고려함으로서 치환되는 리간드를 예측할 수 있다. 총안정화 에너지와 d-궤도함수의 1전자에너지준위는 각종첩모형체계내에서 계산하였는데, 계산결과에 의하면 총안정화에너지 값이 큰 중간체일수록 보다 쉽게 생성된다고 할 수 있다. 결과적으로 총안정화에너지의 상대적인 값은 가장 낮은 에너지의 d-d전이에 해당하는 파장의 빛을 쪼여줄 때 $trans-Cr^{Ⅲ}N_4XY$착물에서 어느 리간드가 우선적으로 불안정하게 되는가를 결정하는데 이용될 수 있으며, $trans-Cr^{Ⅲ}N_4XY$착물의 광수화반응에 있어서 떨어지는 리간드에 대한 이러한 예측은 실험상의 결과와 일치하고 있다.

• Bulletin of the Korean Chemical Society
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• 제34권10호
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• pp.3093-3097
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• 2013

The synthesis, X-ray crystallography, spectroscopic (IR, UV-vis), and electrochemical properties of the title compound, $[H_3O][Cr(dipic)_2][H_3O^+.Cl^-]$ (1), ($H_2dipic$ = 2,6-pyridinedicarboxylic acid), are reported. This complex crystallizes in the monoclinic space group Cc with a = 14.9006(10) ${\AA}$, b = 12.2114(8) ${\AA}$, c = 8.6337(6) ${\AA}$, ${\alpha}=90.00^{\circ}$, ${\beta}=92.7460(10)^{\circ}$, ${\gamma}=90.00^{\circ}$, and V = 1569.16(18) ${\AA}^3$ with Z = 4. The hydrogen bonding and noncovalent interactions play roles in the stabilization of the structure. In order to gain a better understanding of the most important geometrical parameters in the structure of the complex, atoms in molecules (AIM) method at B3LYP/6-31G level of theory has been employed.

• 한국분말재료학회지
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• 제30권3호
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• pp.233-241
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• 2023

In this study, we evaluated the effects of acid leaching on the properties of Cr powder synthesized using self-propagating high-temperature synthesis (SHS). Cr powder was synthesized from a mixture of Cr2O3 and magnesium (Mg) powders using the SHS Process, and the byproducts after the reaction were removed using acid leaching. The properties of the recovered Cr powder were analyzed via X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), particle size analysis (PSA), and oxygen content analysis. The results show that perfect selective leaching of Cr is challenging because of various factors such as incomplete reaction, reaction kinetics, the presence of impurities, and incompatibility between the acid and metal mixture. Therefore, this study provides essential information on the properties under acidic conditions during the production of high-quality Cr powder using a self-propagating high-temperature synthesis method.

• 한국산업보건학회지
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• 제7권2호
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• pp.223-232
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• 1997

The accuracy and precision of a modified method of NIOSH Method 7600 and EPA method 218.6 was determined for analyzing hexavalent chromium, Cr(VI), collected on PVC filter from workplace air. The method was designed to extract from Cr(VI) on PVC filter with a alkali solution, 2% NaOH/3% $Na_2CO_3$, and to analyze it using ion chromatography/visible absorbance detection(IC/VAD). The results and conclusion are as the following. 1. The peak of Cr(VI) was separated sharply on chromatogram and was linearly related with Cr(VI) concentration in sloution. The correlation coefficient was 0.9999 in a calibration curve. The limit of detection was 0.25 $0.25{\mu}g/sample$. 2. The accuracy(% recovery) was 93.3% in a set of sample($9-50{\mu}g$) stored for a day, and 100.1%($10-60{\mu}g$) in another set of samples stored for 2 hours. It is assumed that the difference in recovery by storage time was due to reduction of Cr(VI) to Cr(III). 3. The precision(coefficient of variation, CV) of the method was 0.015 in spiked samples with Cr(VI) standard solution, and 0.010 in spiked samples with plating solution from a chrome electroplating factory. The overall CV in all types of samples was 0.0013. 4. The Cr(VI) was stable in 2% NaOH/3% $Na_2CO_3$ at least for 10 hours. In conclusion, the IC/VAD method is appropriate for determining low-level Cr(VI) in workplace air containing various interferences.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 The 6th International Symposium of East Asian Resources Recycling Technology
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• pp.357-361
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• 2001

The possibility of producing Cr$_2$O$_3$powder from waste magnesia-chromium refractory was investigated by sulfuric acid reaction, alkali fusion, water leaching & purification and heat treatment. The effects of temperature, the amount of NaOH added and the flow rate of air on chromium extraction efficiency in an alkali fusion step were investigated. The fusion product was leached with methanol to solve free-NaOH, and then leached with water to produce a Na$_2$CrO$_4$solution. The purity of chrome(Ⅵ) oxides, prepared both from monochromate with an impurity content and monochromate purified with $CO_2$were also examined. The purified monochromate solution was reduced from Cr(Ⅵ) to Cr(III) with NaHSO$_3$solution. The reduced solution was neutralized with NaOH to produce Cr(OH)$_3$. Water washing was treated to eliminate Na$_2$SO$_4$from neutralized Cr(OH)$_3$slurry. The washed Cr(OH)$_3$was dried and thermally treated to produce Cr$_2$O$_3$powder. The properties like lightness and hue of Cr$_2$O$_3$fabricated in this study were L=47.47, a=-14.40 and b=17.21.